Method for removal of osteal prostheses

ABSTRACT

A relatively massive annular body is driven in radial-mode resonant oscillation by an ultrasonic driver that is fixed to the periphery of the annular body, with the axis of its ultrasonic drive oriented for intersection with the central axis of the annular body. A selected chucking device within the bore of the annular body is adapted to engage part of a prosthetic device, to which the resonant oscillation is imparted, for melting bone cement and for severing bony ingrowth into the prosthetic, thus permitting immediate retraction of the prosthetic from its pre-existing implantation in a living bone.

BACKGROUND OF THE INVENTION

The invention relates to an ultrasonic method and means for removing anosteal prosthesis from cemented installation in a living bone, as in thecourse of revision arthroplasty.

It is known from U.S. Pat. Nos. 4,248,232 and 5,151,099 that ultrasoundmay be used to facilitate removal of bone cement (PMMA) during revisionarthroplasty. Local heating, by preferential absorption of ultrasoundenergy, raises the temperature of a small volume of the cement above theglasstransition temperature, thus allowing the cement to flow and to bemanipulated into a shape and form which may be readily removed from therevision site.

It has also been claimed (Hood, et al., U.S. Pat. No. 5,045,054) thatthe application of ultrasound directly to the prosthesis can break thebond between the prosthesis and surrounding cement or, in the case ofuncemented prostheses, between the prosthesis and in-grown cancellousbone. The direction of applied ultrasonic energy is in line with thecentral axis of an implanted prosthetic device, such as the axis of stemsupport for the ball of a hip-joint replacement. But the in-lineapplication of force, as in the context of the Hood, et al. system, isto require the patient to oppose the force, with inevitable trauma forthe patient.

BRIEF STATEMENT OF THE INVENTION

It is an object of the invention to provide an improved method and meansfor dislodging an installed osteal prosthesis with a minimum of traumafor the patient who is faced with the need of revision arthroplasty.

A specific object is to meet the above object for the case of revisionarthroplasty of a hip-joint prosthesis that has been implanted andcemented in a femur.

It is a general object to meet the above objects with a method andapparatus of reliably high performance without a daunting level ofoperating complexity, which method and apparatus are applicable to thefull variety of currently available prostheses.

The invention in its preferred embodiment meets these objects in anultrasonically driven technique wherein an annular body of relativelygreat mass is solidly chucked around the exposed proximal end of ahip-joint prosthesis which has been cemented in the medullary canal of afemur. In most cases, the exposed proximal end is a sphere or ball atthe projecting end of a stem, all integrally formed with the implantedremainder of the prosthetic device. The annular body is excited intoultrasonic radial-mode oscillation by a driver having a directional axisof mechanical oscillation, wherein the said axis is preferably radiallyinward through body material, toward the body axis, and preferably forsubstantial alignment with the center of the exposed ball or head end ofthe prosthesis to be removed, as for prosthetic replacement in thepatient. In response to such excitation, the annular body reacts withradial-mode resonant oscillation, involving circumferentially continuousapplication of radially modulated squeezing transfer of ultrasonicenergy into the prosthetic at the region of chucked engagement; and, inturn, the prosthetic responds to the radial-mode resonance by suchplastic-deformation of its cemented and/or bony-ingrowth attachment tothe patient's limb, as to locally generate enough heat to melt cementingplastic at interface with the prosthetic, or to mechanically sever bonyingrowth at interface with the prosthetic. The ultrasonically drivenbody annulus is of such design as to selectively accommodate a varietyof sizes of prosthetic-head chucked engagement, as by selected use ofone out of a group of chucks, each of which is configured for clamping adifferent size or shape of prosthetic head. The body annulus will alsoaccommodate a special tool which lends itself to coupling to the buriedend of a broken fragment of a prosthetic shaft, with an ability totransfer sufficient ultrasonic energy through the tool and into thebroken and buried prosthetic fragment, for clean and efficientdislodging and extraction of the buried fragment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which show various illustrative embodiments of theinvention:

FIG. 1 is a view in side elevation, partly broken-away and in section,to show elements of a prosthetic-removal device of the invention;

FIG. 2 is a view similar to FIG. 1 to show a modification;

FIG. 3 is an exploded view of separable parts, as in FIG. 2;

FIG. 4 is a plan view of the device of FIG. 3;

FIG. 5 is a view similar to FIG. 1 to show another modification;

FIG. 6 is a view similar to FIG. 1 to show a further modification;

FIG. 7 is a view in longitudinal section of a tool element usable inconjunction with any of the devices of FIGS. 1, 2, 3, 5 or 6, forremoval of a distal broken end of prosthetic device;

FIG. 8 is a sectional view to show use of the tool of FIG. 7 in thedevice of FIG. 6;

FIG. 9 is an electrical block diagram to show excitation and controlcircuitry for use in any of the disclosed prosthetic-removal embodimentsof the invention;

FIG. 10 is a graph to illustrate a frequency band characteristic ofultrasonic operation, using circuitry of FIG. 9;

FIGS. 11 and 12 are front and side elevation of a tool element forremoving small quantities of cement; and

FIG. 13 is an end view of the tool element of FIGS. 11 and 12.

DETAILED DESCRIPTION

Referring initially to FIG. 1, the invention is shown in application toa radial-mode oscillator comprising an annular body 10 of relativelygreat mass, suitably of stainless steel. Body 10 is of generallyright-cylindrical configuration and has a central bore 11 which isslightly convergent in the downward direction, for the purpose ofcoaction with a chuck or collet member 12. At its upper end, bore 11expands via a counterbore 13 which will accommodate the radially flangedhead end 14 of member 12. The chuck or collet member 12 has a reduceddistally extending lower end which is longitudinally split, as at slit15, to define plural distal fingers, here shown as the two fingers 16,17, in view of the single slit 15.

In the case of FIG. 1, the exposed spherical head or ball 18 of aninstalled hip prosthesis 19 is securely engaged by concave sphericalformations within the distal or finger end of member 12, i.e., withinconfronting internal concave spherical surfaces of the two fingers 16,17, it being understood that the concavities of fingers 16, 17cooperatively define a hemispherical socket against which a ball head 18intimately nests. The external surfaces of fingers 16, 17 preferablyconform to convergence of the body bore 11 such that, once the ball head18 has been inserted into the unstressed socket defined by the internalconcave spherical surfaces of fingers 16, 17, the collet or chuck member12 may be driven downward to securely and circumferentially continuouslyengage and grip the ball head 18. The drive to establish such a grip canbe obtained by hammer blows delivered axially to the flanged upper end14; in the course of such a drive, fingers 16, 17 are inwardly deflectedby wedge action between the convergent concave and convex taperingsurfaces, and it will be understood that in a finally chucked position,as in FIG. 1, the ball head 18 not only has virtually equatorial grip bythe fingers 16, 17, but that this grip is also similarly circumferentialfor axially extending areas above and below the equatorial location.Alternatively, the surgeon may be of the view of hammer blows mightresult in trauma to the patient, in which case a pair of opposedC-clamps applied to squeeze the flange of member 12 with respect to thelower annular surface of body 10 is indicated, for a reduced likelihoodof trauma.

To excite the described body 10 and its securely chucked prostheticdevice 19, an electromechanical transducer 20 is shown secured locallyto the periphery of body 10. Transducer 20 is suitably of thepiezoelectric ceramic variety generally as shown and described (atreference number 1) in U.S. Pat. No. 5,151,099 and in pendingapplication Ser. No. 08/199,112, filed Feb. 22, 1994, to which referenceis made for greater detail. Transducer 20 is cylindrical and has acentral axis 21 of mechanically resonant oscillation, at a frequency inthe range 20 kHz to 40 kHz. The transducer is driven as the electricalload of circuitry to be described later in connection with FIG. 9, butwhich will be indicated here to feature a phase-locked loop forautomatic high-Q tuning over a range of frequencies. The range offrequency adjustment will be understood to be that which best serves themechanically resonant properties of body 10 and its well chuckedconnection to prosthetic 19, and the latter will be further understoodto be in its embedded condition, and to have been the subject of anarthroscopic femoral procedure which now requires replacement.

To give an indication of size, a radial-mode resonant body 10 toaccommodate a ball head 18 of 1-inch diameter is suitably of 5 to 6inches diameter, with an axial thickness of two inches; and transducer20 may suitably be of 3.0 to 3.5-inches overall length and 1.0 to 1.6inches diameter.

A housing recommended for the described parts may generally be as shownand described in pending patent application Ser. No. 08/199,112, as longas the housing enables safe handling during ultrasonic operation. Thephantom outline 22, with elastomeric O-ring supports at 23, 23', 24 willbe understood to be suggestive of such a housing. The housing 22 happensto be removable, cylindrically surrounding the transducer 20 and thusproviding a handle that is mechanically insulated from transducerresonance, and with an upper looping ring portion removably centered onand surrounding the flanged upper end of the chuck or collet member 12.

In operation, excitation of transducer 20 induces radial-mode resonancein body 10 and in the chuck and ball-head elements securely bound withinbody 10. The ball-head is thus induced to track the excursions of thismechanical resonance and to couple them into the volume of theprosthetic 19, with resultant complex mechanical oscillation (featuringmultiple nodes and anti-nodes) at interface between the shank of theprosthetic and such plastic cement or other bond (such as bony ingrowth)that may exist. The result is rapidly, within seconds, to melt cementand to shear bony ingrowth and thus to enable manual retraction of theradial-mode system and the prosthetic 19. In the course of suchretraction, which can be relatively quickly accomplished (in view of thetapered nature of the embedded prosthetic stem), it is optional whetheror not the transducer remains excited, because the embedment bond to thepatient will have been severed.

A note should be made to the effect that the prosthetic appliance 19shown for illustration herein is an integrally formed single piece, sothat a dislodgement is of the entire appliance. There are, however,other appliance structures in use for the same kind of hip-jointreplacement. For example, the ball head 18 may have been a separatelymanufactured ball having a radial bore for "permanent" Morse-taper fitto an otherwise exposed stud which is an integral part of theprosthetic. In that event, the described ultrasonic radial-modeexcitation of the exposed ball of the prosthetic appliance may result indislodging the ball from its Morse-taper fit, thus exposing the taperedstud portion of an appliance that remains embedded in the patient. Forsuch a situation, it will be understood that a second radial-mode systemas described for FIG. 1 may be at hand and equipped with a chuck orcollet having internal concave contours suited for axially extensive andfor virtually circumferentially continuous engagement with the otherwiseexposed stud end of the prosthetic. Ultrasonic excitation of the chuckedstud will then achieve the same desired result of inducing suchmechanical action at the embedded interface or interfaces within thebody as to enable quick and efficient retraction of the prosthetic.

Once the prosthetic has been removed, personnel aiding the surgeon canaddress the problem of disengaging the chuck and the chucked prostheticfrom the radial-mode body. To this end, angularly spaced plural tappedbores 25 in the flanged end of the chuck may be threaded with bolts (notshown), for axially jacking reference to the flat inner annular end ofthe counterbore 13. Upon a sufficiently jacked displacement, the chuckaction becomes dislodged and the prosthetic and the chuck 12 may beremoved from each other and from body 10.

The embodiment of FIG. 2 represents slight modification from what hasbeen described for FIG. 1, and the same reference numbers are re-usedwhere possible. The chief difference in FIG. 2 is that the directionalaxis 21' of ultrasonic excitation by transducer 20 is not only orientedradially inward, but axis 21' is also inclined downwardly forintersection at or near the spherical center of the concave sphericalinner surfaces of fingers 16, 17, thus at or near the spherical centerof a ball or ball head 18 chucked thereto. To this end, the annular body10' for excitation into radial-mode mechanical oscillation has an outersurface 27 which is frusto-conical so that the inclined driving end faceof transducer 20 may be mounted to a locally milled flat 27' in thefrusto-conical outer surface. Further, FIG. 2 shows an additionalcounterbore 28 at the lower end of the central bore of body 10' toprovide greater concentration of ultrasonic energy from body (10')structure to an exposed ball head and associated bone structure (notshown in FIG. 2). Action and use are otherwise as indicated for thestructure of FIG. 1.

FIGS. 3 and 4 depict in greater detail an alternative version of themodification of FIG. 2, wherein the axial direction 21' of ultrasonicexcitation from transducer 20 into body 10 is again radially inward andalso downwardly tilted for anticipated near-center delivery to thespherical center of a chucked ball head 18. In FIG. 3, body 10 is againcylindrically annular as in FIG. 1, and the driving end of transducer 20is received in a shallow, suitably inclined local bore in the peripheryof body 10, for flat-to-flat end-face delivery of mechanical oscillationto body 10; in FIG. 3, a reduced stud portion 30 of the driving end faceof the transducer is shown in tightly threaded engagement with a tappedbore at the base of the transducerseating bore in body 10.

The greater detail of FIG. 3 enables identification of further featurescommon to all embodiments of the present invention. The threadedmounting via a stud is at 30, with otherwise flat-to-flat end interfacefrom the transducer to the radial-mode body; such a flat-to-flatinterface can be taken as presently preferred for all embodiments. Thelength L of the transducer should be an integer number ofhalf-wavelengths of sound transmission in the medium of the transducer;this medium is suitably a conventional sandwich of aluminum alloy andstainless steel plate elements, except of course for the piezo-electricceramic disc and its waferthin electrodes which are at outward offsetfrom the central transverse plane of the transducer. The mean diameterD_(m) of the radial-mode body 10 is preferably such as to account for amean geometrically circumferential extent (i.e., at diameter D_(m))which is approximately an integer multiple of said wavelength.¹ And theslightly convergent taper angle α within the bore of body 10 ispreferably in the range 1° to 2° Anticipating substantial sphericalconcave-to-convex surface light engagement of the chuck or colletfingers 16, 17 to the ball or ball head 18, the concave sphericalsurfaces of fingers 16, 17 are preferably generated when fingers 16, 17are radially inwardly displaced to the extent of an ultimately chuckedstate; and the outer-surface contouring of the chuck fingers 16, 17 issuch as to develop progressive inwardly cantilevered bending to lockonto a ball or ball head 18 in the course of hammering or other axiallyjacked displacement into the fully chucked position shown for allembodiments except for the exploded diagram of FIG. 3.

Finally, FIG. 3 illustrates the environment for use of a radial-modesystem for all embodiments of the invention, namely, that the taperedstem portion 31 of the involved prosthetic device 19 has the environmentof plastic cement 32, securing the prosthetic to and within anintramedullary cavity in a suitably cored and otherwise preparedproximal end of a femur 33. The relatively massive use of plastic cement32 will be understood in FIG. 3 to have been exaggerated, and it will beunderstood that very often in the preparation of a femur to receive ahip-joint prosthetic 19, the stem 31 will have been installed at leastin part in such direct adjacency to bone tissue as to have involvedbony-ingrowth into the prosthetic; still further, the installation ofprosthetic 19 may have been so installed in the femur as to have reliedsolely on bony ingrowth for fixation, in which case, radial-modeexcitation of the body 10 will sever the bony ingrowth to permit removalof the prostheic.

In the embodiment of FIG. 5, the radial-mode body 10 isright-cylindrical and of axial thickness matching the diameter of thetransducer 20. There is no counterbore into which the flanged head ofchuck 12 may be accommodated (as at 13 in FIGS. 1, 2 and 3), but thereis a lower counterbore 28 which enables clearance for chucked clampingof a prosthetic ball or ball head 18 with its spherical centersubstantially on the strictly radial transducer axis 21 of ultrasonicmechanical oscillation. Dimensioning applied to FIG. 5 identifies thecylindrical outer diameter D of body 10 and the mean diameter D_(m).Further dimensioning at Δ identifies the fact that the body cylinder ofdiameter D is locally milled to a chordal flat (of radial depth Δ) forestablishing a flat interface between transducer 20 and body 10, thesame being tightly secured by threaded means 30.

The embodiment of FIG. 6 illustrates that a radial-mode annular body 40of the invention need not be geometrically cylindrical, and it alsoillustrates that plural ultrasonic transducers may be provided atangular spacing around body 40, all with their respective axes ofmechanical oscillation directed to substantially the center of a ball orball head 18 of an implanted prosthetic 19. As shown, the plurality oftransducers is two, at 180° spacing about the central axis of body 40.The geometry of body 40 may be described as annular, with a central boreand chucking or collet means 12 as previously described. The annularbody 40 features an upper concave frusto-conical end face 41 that isaxially spaced from a lower convex frusto-conical end face 42. The outersurface of body 40 is also frustoconical except for local chordal flats43a, 43b to accept the flat-interface relation of transducers 20a, 20bat their respective connections to body 40. Preferably, the concaveslope of upper surface 41 is at greater offset from a radial plane withrespect to the central axis of body 40 than is the lesser such offset inthe case of lower surface 42. This relationship establishes thepresently preferred shape of body 40 as a dish wherein axial thicknessreduces in approach to the central bore to which the chuck 12 is fitted,thus enabling radial-mode oscillation to bring resonant energy to evengreater convergence at the desired locus of energy transfer toprosthetic 19. For purposes of deriving purely axial jacking force todislodge a clamped condition of chuck 12, a small local fillet 44, onefor each of the threaded jack bores 25 of the chuck flange, enablesinserted jack bolts to be driven perpendicular to corresponding fillets44.

In the removal or attempted removal of a hip-joint or other prostheticfrom a patient, it sometimes happens that the stem of the prostheticbreaks or is found to have been broken, thus leaving a distally embeddedfragment of the stem, as shown at 50 in FIG. 8. At the point in timeillustrated by FIG. 8, it will be understood that bone cement within theproximal end of a femur 52 has been selectively removed to establish anenlarged opening 53, i.e., enlarged from the socket of bone cement leftupon removal of the proximal part of the prosthetic, and it will befurther understood that this enlargement has been achieved not only asfar as the embedded broken piece 50 but also to the extent therebeyond.Bone-cement removal tooling as described in copending patent applicationSer. No. 08/199,112, filed Feb. 22, 1994, now abandoned, is ideal forrapid and effective bone-cement removal to achieve the describedenlargement, including to the predetermined depth d₁ beyond the locationof the break which produced the embedded fragment 50.

A tool bit 80, based on the technology described in said copendingpatent application, is shown in FIGS. 11 and 12. This tool bit featuresa distal-end claw formation 81 which may be used to melt and extractcement in small quantities from and around the periphery of the end ofthe fragment 50, to provide the enlarged opening 53. The tool comprisesa stem 82 wherein the claw formation 81 at its distal end is a smallsaucer-shaped cup, having longitudinal apertures 83 therethrough; whenthe cup at 81 is driven in longitudinal oscillation, by reason ofultrasonic longitudinal vibration of stem 82, cement melts at and nearthe distal side of the cup, and melted cement passes through theapertures to accumulate within the cup. The tool may be withdrawnperiodically to extract cement or other material and thereby to furtheraid formation of the enlarged opening. In addition, when withdrawing thetool bit, its proximally facing peripheral lip may be a relatively sharpedge, permitting it to serve a scraper function in the process offorming the enlarged opening, the scraping being against the outersurface of the broken fragment 50, to enable direct grasping engagementof an extraction tool to the broken fragment.

Having thus prepared the enlargement 53 in bone cement at the proximalend of femur 52, and to the depth d₁ beyond the break responsible forthe embedded fragment 50, all is in readiness for use of a special toolbit as shown in FIG. 7, as a replacement for the chuck or collet element12 in any of the embodiments described in connection with FIGS. 1, 2, 3,5, and 6 above; and in FIG. 8, the tool bit of FIG. 7 will be recognizedin substitution for the chuck 12 of FIG. 6.

Briefly, the tool bit of FIG. 7 is suitably of stainless steel andcomprises a flanged head 55, integrally formed with plural elongate,relatively massive but tweezer-like legs 56, 57. The outer diameter D₂may be cylindrical and thus constant in manufacture of the tool bit.Within this cylindrical outer-surface profile, a gradually tapering boreestablishes concave inner-surfaces 56', 57' of the legs 56, 57, allexcept for the distal remainder d₂ which is characterized by shortdistally convergent concave profiles 56", 57" within the distal ends oflegs 56, 57. The cylindrical diameter D₂ is selected to permitinsertional entry of the distal ends of legs 56, 57 through the upperend of the convergent central bore of the radial-mode body, the same tobe inwardly cammed in the course of full insertion through this centralbore. This inward camming action deflects legs 56, 57 toward each otherand in all likelihood into radially loaded mutual contact of theirdistal ends by the time these distal ends have been extendedsubstantially fully beyond passage through the bore of body 40. At thispoint it is a simple matter to compliantly spread apart the distal endsof legs 56, 57, as by inserting and twisting a screwdriver bladetherebetween, the thus achieved spread being such as to permit insertionof the distal ends of legs 56, 57 into the enlarged opening 53 and pastthe upper end of the embedded broken fragment 50. Such insertion may beto the extent 2 beyond the detection of initial contact with fragment50, whereupon the screwdriver or other spreading device may be removedto permit legs 56, 57 to apply a compliantly stressed grasp of theproximal end of fragment 50. At this point, the grip of legs 56, 57 onthe fragment 50 is sufficient for direct transfer of ultrasonic energyfrom the radial-mode body 40, and via the tool bit of FIG. 7, to thefragment 50, whereby to impart ultrasonic energy to the fragment formelting or breaking its interface with bone cement or with bonyingrowth, as the case may be. And of course, when thus melted or brokenat this interface, the embedded fragment 50 is in readiness forimmediate extraction, using the same grasp by legs 56, 57.

The various embodiments of the invention will be seen to provide amethod and apparatus for the removal of osteal prostheses, when exposedor broken as a fragment that may remain buried and embedded within bone.Importantly, the method and apparatus are served by a high-massradial-mode resonator compressionally coupled to the spherical head, orcylindrical or Morse-tapered proximal end, of the prosthesis. The systemmeets two principal criteria: the radial-mode resonator permits axialattachment of a rigid mass to the prosthesis, without thetrauma-inducing prospect of direct ultrasonic drive of the prostheticdevice distally with respect to the central axis of the ball orball-head and its embedded stem. This result is achieved with arelatively small shift in resonant frequency, and it is compatible withthe use of a fully automatic tuning system such as that which isschematically presented in FIG. 9.

FIG. 9 depicts excitation circuitry wherein phase-locked control expandsthe bandwidth tolerance of the system to shifts in mechanical resonancefrequency, within limits, for a given setting of circuitry parameters.Specifically, a power-supply unit 60 may rely upon conventional a-cpower, available at 61 as from a household wall outlet, and unit 60derives both high-tension (HT) d-c and low-tension (LT) d-c supplies toautomatic-tuning circuitry, wherein ultrasonic excitation voltage isdelivered to the involved transducer 20, here symbolized as "load" 62.The HT supply is interrupted by phased high-frequency switching devices63, 64, producing a square wave across the primary of an outputtransformer 66, the frequency of which is determined via a first input67 suitably amplified at 68 from a phase-locked loop (PLL) at 69, andvia a second input 70 from a microprocessor (μP) controlled LCR network71; the LCR tuning circuit 71 is associated (via connection 74) with alow-voltage secondary winding of output transformer 65, and the tuningfunction of the microprocessor (μP) may be defined in software containedin an EEPROM or similar device, allowing automatic tuning over a widefrequency range. In the supply from transformer 65 to the load 63,matching values of inductance (L) and capacitance (C) are chosen toensure sinusoidal current and voltage waveforms in the load 62 and toprovide an essentially constant load-current characteristic. Feedback inline 72 reflects instantaneous output from the impedance-matchingnetwork 73 and is continuously supplied to the phase-locked loop means69. The net result is indicated by the solid-line curve of FIG. 10,wherein phased-locked automatic tuning is seen to be ensured for theresonant-frequency band from f₁ to f₂, indicating a span of mechanicalresonance that is held in tune without need for manual adjustment; forcomparison, the same structure and excitation values, without thebenefit of the indicated phase-locked loop and automatic tuning are tobe understood as producing the essentially single-tuned frequencycharacteristic that is shown by the phantom-line curve of FIG. 10.

What is claimed is:
 1. The method of removing a bone-implantedprosthetic from an installed situs of cemented or bony-ingrowthretention within a living bone, wherein at least a portion of theprosthetic is externally exposed with respect to the bone, which methodcomprises the steps of:(a) selecting an annular body of a materialcapable of radial-mode resonant oscillation in the frequency range 20kHz to 40 kHz, said body having a central axial bore of size toaccommodate an exposed portion of the prosthetic; (b) securing theexposed portion of the prosthetic with substantially completecircumferential continuity within said bore; and (c) ultrasonicallyexciting said body into radial-mode oscillation by generally radiallyinwardly directing mechanical-displacement energy at a peripherallocation on said body, said driving energy being imparted to said bodywithin said frequency range.
 2. The method of claim 1, wherein step (c)is concurrently performed at each of a plurality of angularly spacedperipheral locations on said body.
 3. The method of claim 1, wherein theexposed portion of the prosthetic is the ball head of a hip-jointprosthetic, and wherein the generally radially inward direction of step(c) is also directed on a geometric axis for intersection with the ballhead of the prosthetic.
 4. The method of claim 1, wherein the securingof step (b) is such as to apply a radially inward compressive preload onthe exposed portion of the prosthetic, in reaction to hoop-tension inthe annular body.
 5. The method of removing a bone-implanted prostheticfrom an installed situs of cemented or bony-ingrowth retention within aliving bone, wherein at least a portion of the prosthetic is externallyexposed with respect to the bone, which method comprises the stepsof:(a) selecting an annular body of a material capable of radial-moderesonant oscillation within an ultrasonic frequency range, said bodyhaving a central axial bore of size to accommodate an exposed portion ofthe prosthetic; (b) securing the exposed portion of the prosthetic withsubstantially complete circumferential continuity within said bore; and(c) ultrasonically exciting said body into radial-mode oscillation bygenerally radially inwardly directing mechanical-displacement energy ata peripheral location on said body, said driving energy being impartedto said body within said ultrasonic frequency range.
 6. The method ofclaim 5, wherein step (c) is concurrently performed at each of aplurality of angularly spaced peripheral locations on said body.
 7. Themethod of claim 5, wherein the exposed portion of the prosthetic is theball head of a hip-joint prosthetic, and wherein the generally radiallyinward direction of step (c) is also directed on a geometric axis forintersection with the ball head of the prosthetic.
 8. The method ofclaim 5, wherein the securing of step (b) is such as to apply a radiallyinward compressive preload on the exposed portion of the prosthetic, inreaction to hoop-tension in the annular body.
 9. The method of removinga broken fragment of a bone-implanted prosthetic from an installed situsof cemented or bony-ingrowth retention within a living bone, wherein thebroken fragment is buried within the bone and no part of the brokenfragment is exposed externally with respect to the bone, which methodcomprises:(a) selecting a first tool adapted for longitudinaloscillatory displaceability and sized to remove cement or bony-ingrowthmaterial to a predetermined depth surrounding a proximally exposed endportion of the fragment, and ultrasonically exciting said tool to removesaid material to said predetermined depth, thereby exposing saidproximal end to said depth; (b) selecting an annular body capable ofradial-mode ultrasonic oscillation, said body having a central axialbore that is characterized by a frustoconical taper; (c) selecting asecond tool having a proximal-end base portion to lap and fit to thebore of said annular body, said second tool having two elongate fingerelements integral with said base end, said finger elements havingdistal-end formations adapted to radially clamp the exposed proximal endof the broken fragment when the base portion of said second tool isfitted to the tapered bore of said annular body; (d) engaging thedistal-end formations of said second tool to the exposed proximal end ofthe broken fragment, and fitting the base portion to the tapered bore ofsaid annular body; and (e) breaking any remaining cemented orbony-ingrowth engagement of the broken fragment within the bone, byultrasonically exciting the exposed proximal end of the broken fragmentvia radial-mode excitation of said annular body with resultingultrasonic excitation of said second tool.